AGM HK416 Gearbox sticks
 

I have an AGM HK416 which doesn't fire. The piston moves back partially and then just stays there, pulling the trigger results in a motor pushing against an immovable object type sound. I've downgraded the spring in case the springw was to powerful for the motor and i've stuck in an EG1000, still same thing happens. I've had the gearbox apart and back together again, i'm pretty new at gearbox maintenance but i sort of know my way around them and i can't see anything wrong.

Help!

Oh yeah forgot to mention i've swapped the battery/bypassed the fuse etc. still nothing.

That could be caused by several thing..... but IMO I think it's the motor height beeing too high, a discharged battery, or a too tight shimming....

I've played with the motor height, the gears spin fine when I build the gearbox with just the gears and i've tried a variety of newly charged batteries...

Motor too high probably would not let it turn that much. Shimmed too tight is very possible.
Definitely check your battery.
Assuming battery is ok, make sure you're not shorting anything and you have a good connection where you removed the fuse.

Are there any new parts in the gun? I've had pistons that weren't quite right that forced the teeth to lockup halfway throught the cycle.

Open the box, remove the anti-reverse and tappet spring, then spin it by hand while trying to keep the piston/gears aligned as they would be if the box was closed. Feel for tight spots. Check the teeth in your gears to make sure nothing is binding there.
Make sure your spring can actually compress into your piston.

Good luck!

Cool, something i can actually do to try and sort it makes me feel a lot more positive. I'll give that a go, thanks. BTW i all ready swaped out the piston, no change..

Try this. Remove the gearbox from the gun, attach the pistol grip directly with motor and all and see if it fires that way out of the gun. If it does, I think I know what your problem may be.

Just tried this, problem still occurs...

Tried taking out the tapet spring and antireversal latch and winding with finger and everything seemed fine, obviously I removed the spring to to do this.

The problem is very similar to this one http://www.airsoftcanada.com/showthread.php?t=83013

Thanks all for your help

Is this a used motor, the motors can wear out and not pull the piston even though it will still spin when connected to a battery source. Possibly try a different motor to test that theory.

Also what size, make and type of battery are you using. If using mini go for a large and see what happens. Many cheap mini's cannot pull stronger springs. Also if the battery is not charged correctly or damaged this lack of spring compression can occur.

Try a proven motor and someones reliable large battery, once you have ensured the previous shim job was completed correctly

do you have any bearing spring guide or bearing head in here...

I'm using an 8.4 volt crane stock battery but it's agm so i guess not great quality. Tried different motors. I've used a bearing and a non-bearing head.

what fps does it shoot (what spring)? That battery is sort of weak, but if its poor quality, could be even weaker. Might not have the power

Was thinking of sticking a 9.6 in there but the only one i can find locally for crane stocks is 2 sticks of 4 batteries which seems pretty useless as surely it won't fit in a crane stock...

I'll test it with a 9.6 though. The box says the gun is like 400fps but the spring has been downgraded.

http://forum.turnbridge.com/uploads/...1243343983.jpg

http://forum.turnbridge.com/uploads/...1243344047.jpg

http://forum.turnbridge.com/uploads/...1243344059.jpg

Some pics i took of the gearbox just to make sure it's all in order.

If i stick a screwdriver in the port when the piston's jammed back and force it back while pulling the trigger it fires and then it'll shoot 3 or 4 times but then jam again. Pretty much sounds like the spring is to powerful still right?

I'm pretty desperate for it to work for tonight, what would you guys say about cutting the spring down slightly?

Don't cut the spring yet, my best guess is that it is the battery. Try a 9.6 or 10.8 forget about fitting the crane stock for now just try to get it cycling. If the bigger battery does it you know the exsisting battery is dead or underpowered. This is a common mistake most people make and don't try new batteries before ripping apart the gear box. It happened to me (years ago) and a new proven 9.6v battery like a sanyo nicad made the mechbox run sweet. A no name cell custom 9.6v NIMH battery could not even cycle the piston and it would jam.


Your pictures are kind of fuzzy, but are the wires stripped or bare close to the motor opening? They look like they possibly could be. If they are it could be shorting out and why it will not cycle

When you put it together with just the gears in, did you screw down the mechbox?

This is a really good point, if you don't and just finger hold it, it is not the same. Unless you put the screws back in you can never be sure the gears are free wheeling because everyones "grip" is different when thet just hold a mechbox together.

Edit:

Here is a good link http://pageproducer.arczip.com/daedalus03/shim.html

It sounds exactly like your battery is too weak.

Throw a 9.6v large on there and it will work again.

If it worked with this same spring before, you have done something to make the gears tighter that makes the motor have to work too hard to move the gears. Improper shimming (what everyone has said about putting screws in first to see how well gears spin freely) probably. Or your current battery might just be on it's last legs and doesn't have enough discharge rate to turn your motor over at the very peak of spring compression where the most torque is needed.